Securities (Additional Information) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Schedule of Investments [Line Items]
Unrealized gains on securities available-for-sale included in accumulated other comprehensive income, net of deferred taxes	$ (10,300,000)	$ (6,085,000)
Unrealized gains on securities available-for-sale included in accumulated other comprehensive income, deferred taxes	$ 2,821,000	3,227,000
Number of investment securities which had unrealized losses for twelve months or longer | security	209
AFS and HTM securities in Continues Unrealized Loss Position	$ 741,200,000	658,500,000
AFS and HTM Securities Unrealized Loss Accumulated in Investments	14,500,000	13,200,000
Investment securities with unrealized losses for twelve months or longer	398,360,000	103,708,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11,172,000	3,850,000
Investment securities with unrealized losses that are considered temporary	722,438,000	615,699,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In Investments	(14,261,000)	(12,536,000)
Other than temporary impairment losses		0
Federal Home Loan Bank Stock	18,300,000	17,800,000
Federal Reserve Bank Stock	5,400,000
Dividend income from subsidiary	1,100,000	1,000,000	$ 579,000
Carrying value of investments sold	19,500,000	28,800,000	12,400,000
Security pledged as collateral, amortized cost	702,500,000	597,300,000
Security pledged as collateral, fair value	$ 691,200,000	$ 589,700,000
Unrealized Loss as a Percent of Amortized Cost	2.00%	2.00%
Gross realized gains	$ 869,000	$ 125,000	221,000
Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Investment securities with unrealized losses for twelve months or longer	398,400,000	103,700,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11,200,000	3,900,000
Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Unrealized gains on securities available-for-sale included in accumulated other comprehensive income, deferred taxes	2,800,000	3,300,000
Gross realized gains	$ 855,000	$ 51,000	$ 4,000